1. Field of the Invention
This invention relates to the control of reversibile motors and more particularly to the interconnection between a reversible motor and a remote control unit in panning/tilt head type systems.
The invention has particular application to the control of pan/tilt heads used in surveillance systems for controlling the direction of rotation of the head during both automatic and manual scanning modes of operation in which the head is caused to rotate bi-directionally or alternatively oscillate within a predetermined sector.
2. Related Art
U.S. Pat. No. 4,293,876 is directed to remote-controlled television monitoring systems in which a transmitter unit provides control signals to a video control circuit in a receiver unit which controls the positioning of a camera unit mounted on a pan/tilt unit. A circuit diagram of a video control circuit is illustrated in FIG. 8 of the patent. As set forth at column 7, lines 29 to 55, the function of the video control circuit is to selectively apply a positive or negative control voltage to a motor. A significant feature of the video control circuit disclosed in this patent is that it enables two control signals, namely either a positive or a negative voltage, to be applied on a single wire, which is advantageous in allowing the transmitter to be remotely located from the area being monitored by the camera unit.
Those of ordinary skill in the art of motor control circuitry will readily recognize that the control of the panning motor of a surveillance unit will require the use of two video control circuits, only one of which is disclosed in the aforementioned patent. That is, two such control circuits are required to provide both manual and automatic control either in a left/right operation or continuously oscillating mode. Furthermore, at least five conductors will be required, one each to provide respective plus and minus voltages, one for the auto/manual switching function, one to provide signals for left and right movements, and one line for controlling the speed of the scanning motor.
U.S. Pat. No. 3,530,268 describes an electrical circuit for control of an electrical motor and is illustrated in FIG. 8 of the patent. Closure of a main motor switch causes a motor-driven mechanism to rotate a shaft through a given angular movement until a spring arm engages a lever, which in turn actuates a switch to open one of two alternate motor circuits, and simultaneously therewith to close the other of the alternate motor circuits, thereby causing the motor-driven mechanism to rotate in the opposite direction.
The stud shaft eventually engages the lever to reverse the closed and opened positions of the respective switches in each of the alternate motor drive circuits which causes the motor-driven mechanism to rotate in the reverse direction.
It is readily apparent that this circuit has at least the disadvantages of requiring two motor drive circuits and center-tapped a transformer.
U.S. Pat. No. 4,080,629 discloses movement of a surveillance camera and which requires at least six conductors for effecting control of such movement.